For preventing passage of gases, vapors or flames from one portion of conduit system to another; Required in Class I, Division 1 and 2 locations where 2 IN or larger conduit enters enclosure, fitting housing terminals, splices or taps; Required in Class I, Division 1 and 2 locations at the boundary where conduit leaves classified location; Required in Class I, Division 1 and 2 locations where two or more enclosures are connected by 36 IN or less conduit, seal must be located within 18 IN of either enclosure; Required where cables (which exceed rate of gas or vapor transmission permitted for seals) are used in Class I, Division 2 locations; Explosionproof, dust-ignitionproof, raintight; Smooth, rounded integral bushing in each hub protects conductor insulation; Accurately tapped, tapered threads for tight, rigid joints and ground continuity; Removable nipple in ma